A variety of retractors for seat belts have heretofore been proposed and put into practice. In recent years, emergency locking retractors (ELR) for seat belts have also been proposed. These emergency locking retractors are provided with a mechanism capable of locking a seat belt in case of emergency, e.g. when acceleration exceeds a threshold value. On the other hand, a number of reseaches and developments have been made in automobile industries for fuel economization, enhancement of running performance and keeping of a large interior space. For these studies, individual automobile parts are requested to be lightweight and compact.
Under such circumstances, emergency locking retractors for seat belts are also requested to be lightweight and compact so that a part of the metal parts used heretofore has been substituted with parts made of a synthetic resin to lighten the weight. For example, a metallic winding reel was made lightweight by a method wherein the reel was formed with a synthetic resin and the center of the reel was provided with a metallic reinforcing element. In recent years, emergency locking retractors for seat belts, which are compact as a whole and have a small number of parts have been developed and actually put into practice wherein a spindle having rectangular ends is used to swing a swing member mounted loosely outside the spindle and the swing member is engaged and locked with a locking means fixed to a housing. Emergency locking retractors having such structure are disclosed, for example, in Japanese Laid-open Patent Appln. No. Sho. 57-128170 (U.S. Pat. No. 4,508,289) and Japanese Laid-open Patent Appln. No. 58-94865 (U.S. Pat. No. 4,453,681).
However, the prior art emergency locking retractors disclosed in these publications are very complicated because the shape of a hole used in the swing member for loosely inserting the spindle must be precise as the swing of the swing member is controlled by such a complicated shape, thus making the manufacture of the emergency locking retractors troublesome and the function thereof less reliable. When the swing member is engaged with the locking member in these prior art retractors, the teeth of these members sometimes abut against each other at the top thereof and are not correctly engaged with each other. Under such condition, disengagement occurs when a strong force is exerted to a webbing, with the result that the webbing may significantly be pulled out and the emergency locking retractor function is then lost.
In the emergency locking mechanism of this type, the swing member must also be considered as a part of the inertial means. In these retractors wherein no consideration is paid to this problem, however, the center of gravity of the inertial means does not correspond to the rotation center of a webbing-winding shaft so that sensitivity of inertial locking may vary according to the location of the shaft in rotation, thus influencing the stability of performance. Further, the load capacity of these retractors varies according to whether the position of the longer edges of the spindle of the webbing-winding shaft are located parallel or vertical to the direction of load. When the longer edges are located in a position which is vertical to the direction of load, the bending strength of the spindle itself is weakened as well so that the locking member and the swing member may be disengaged by deformation such as twisting of a resinous portion in the winding shaft or wherein the load capacity is considerably reduced. In the retractors disclosed in Japanese Laid-open Patent Appln. No. Sho. 58-94865, the rotation of the winding shaft is restrained so that the swing member may be moved upward from the fixed position for engagement such that the danger of disengagement may result. Further, the shape and structure of a hole for accepting the spindle are too complicate for controlling the swing member so that the manufacture of the retractor is made troublesome and some problem arises in reliability of the function, as described above.
Even if the prior art emergency locking retractors for seat belts are made lightweight by the use of parts made of a synthetic resin, however, there is still room for improvement by avoiding the necessity for high precision in their manufacture, stabilizing inertial locking, by enhancing load capacity in the locking member and by simplifying the structure. Thus, there is a demand for developing a new emergency locking retractor for seat belts which overcomes these drawbacks.